This invention pertains to non-destructive acoustic monitoring methods and more specifically to such methods that can be employed to monitor the gas pressure within a hermetically sealed enclosure.
A number of articles of manufacture contain a pressurized gas as part of their operative embodiment. For example, as is well known in the art, a number of fuel elements for nuclear reactors are pressurized during manufacture to provide support for the fuel element cladding during operation under irradiation and external coolant pressure. To assure the quality of the manufactured items as well as the integrity of such items during periods of storage it is desirable to employ non-destructive testing techniques to measure the internal pressure of such items before application in their intended environment.
Methods of non-destructively measuring pressure are particularly important in the manufacture of nuclear fuel elements because of the adverse effects associated with fuel element failures during reactor operation. Testing methods presently under consideration call for destructively testing a sampling of fuel elements in each manufacturing lot, or implanting special pressure indicating devices in or on randomly selected elements. In either case, such methods rely on statistical data which may well prove unreliable. In addition, the industry is presently experimenting with a method that requires dipping of the plenum end of the fuel element into a liquid nitrogen bath to locally chill the gas in the plenum and cause a decrease in the internal gas pressure. The decrease in pressure apparently produces changes in the overall dimension of the element which can be related to the internal pressure. Aside from the question of accuracy, serious problems are encountered by subjecting various critical weldments on the fuel element to extreme thermal transients as anticipated by this experimental method.
Accordingly, a new method is desired capable of non-destructively measuring gas pressure within a hermetically sealed enclosure.